lnterrelated functions of hemostatic, kinin-releasing, and fibrinolytic enzymes in plasma and the serum complement system will be examined to gain insight into the ways in which some of those enzymes are regulated by the serum C1-inhibitor, which regulates several such enzymes but is critical to the regulation of C1, the activated first component of complement. In addition, hemostatic events involving high molecular weight kininogen may affect vascular function, and the interactions between this kininogen and endothelium will be examined. To do this, several approaches will be used: 1. Purified normal C1-inhibitor will be examined to determine if different domains of the molecule may participate in site-specific interactions with the plasma proteases known to be regulated by this inhibitor. This possibility is likely because our earlier studies showed heterogeneous behavior of abnormal C1-inhibitor proteins from persons with hereditary angioneurotic edema with respect to each of the enzymes regulated by normal C1-inhibitor. To do this, fragments of normal C1-inhibitor generated with cyanogen bromide, or by limited proteolytic digestion, will be examined for their inhibitory activity and their ability to form complexes-with these proteases (factor Xlla, kallikrein, plasmin, C1s. 2. There are multiple possible explanations for altered expression of the C1-inhibitor gene in hereditary angioneurotic edema. One approach to be used in this laboratory to gain insights into this problem will be to compare mRNA from peripheral blood monocytes of normal persons to that from persons with different types of hereditary angioneurotic edema. Both the quantity and quality of mRNA from these patients will be compared to that from normal individuals. 3. Cultured human umbilical endothelial cells will be tested for antigens located on the heavy or light chains of human high molecular weight kininogen. Since light chain participates in binding to certain substances and in generating clot-promoting activity, it might be identified on endothelial membranes, and might transfer to these cells under definable states in which its function would be provoked. Additional studies will examine the ratios of plasma concentrations of light and heavy chain antigens of HMWK in plasma from normal persons- and those with pathologic states involving the vasculature.